Brush seals are used to minimize leakage through a gap between two components, wherein such leakage is from a higher pressure area to a lower pressure area. Brush seals have been used, or their use proposed, in rotating machinery. Such use includes, but is not limited to, turbomachinery including steam turbines and gas turbines used for power generation and gas turbines used for aircraft and marine propulsion. It is noted that brush seals minimize the leakage of steam in steam turbines and minimize the leakage of compressed air or combustion gases in gas turbines.
A steam turbine has a steam path which typically includes, in serial-flow relationship, a steam inlet, a turbine, and a steam outlet. A gas turbine has a gas path which typically includes, in serial-flow relationship, an air intake (or inlet), a compressor, a combustor, a turbine, and a gas outlet (or exhaust nozzle). Gas or steam leakage, either out of the gas or steam path or into the gas or steam path, from an area of higher pressure to an area of lower pressure, is generally undesirable. For example, gas-path leakage in the turbine or compressor area of a gas turbine, between the rotating tips of the turbine or compressor rotor blades and the circumferentially surrounding turbine or compressor casing, will lower the efficiency of the gas turbine leading to increased fuel costs. Also, steam-path leakage in the turbine area of a steam turbine, between the rotating tips of the buckets (i.e., blades) and the circumferentially surrounding casing, will lower the efficiency of the steam turbine leading to increased fuel costs.
Conventional brush seal designs have been proposed for use in such applications. The brush seals have wire or ceramic bristles conventionally welded or otherwise affixed to a backing plate. To improve performance, such brush seals typically align their wire bristles to contact the rotating tips of the blades/buckets at an angle between generally forty-five and generally sixty degrees with respect to a radius line from the center of the rotor to the point of bristle contact. However, the rotating tips of the blades/buckets typically present a bumpy surface since circumferentially adjacent blades/buckets typically are of slightly different radial lengths, such differences being sensed as bumps by the bristles. Such bumps cut and unevenly wear the free end of the bristles which results in poor sealing. It is noted that increasing the previously-described angle of the bristles beyond generally sixty degrees results in a very long bristle which is too flexible to provide good sealing.
What is needed is an improved brush seal which will maintain its sealing qualities even when used against bumpy rotating surfaces such as the shrouded free ends of gas turbine blades or steam turbine buckets.